Light emitting diodes (LED's) are fast becoming the preferable light source for automotive lighting applications, as they consume less power but provide light output which is becoming acceptable for such applications. When LED's are employed in headlamps (i.e., headlights), several requirements must be met. Specifically, the beam pattern provided in road illumination should have a certain amount of vertical spread as well as a certain amount of horizontal spread. At the same time, a vertical cut-off should be provided to minimize glare to oncoming traffic.
Generally, headlamps for motor vehicles can be characterized as reflector-type headlamps or projector-type headlamps. Reflector-type headlamps employ a specially structured reflector unit which collects and redirects light from the light source, and are especially constructed to focus the light as well as provide the necessary beam spread. In projector-type headlamps, a standard projector unit employs a reflector that collects light from the LED light source and provides the beam spread. Light from the reflector passes through a condenser lens which simply and projects light from the reflector for illuminating the roadway. In a direct projector unit, no reflector is employed and a limited amount of control, is available over the beam spread through selection of the light source and its position relative to the condenser lens.
The condenser lens is an imaging optic which simply projects the image placed at its focal point onto the road, thereby creating a beam pattern simply by inverting the source (left is right and up is down). These condenser lenses are aspheric lenses which are axi-symmetric and obtained by a surface revolution of a two-dimensional curve about the optic axis (i.e., a longitudinal axis extending through the lens center). To obtain control over the beam spread characteristics, the reflector of the standard projector-type headlamp is elongated, primarily in the horizontal direction, in order to obtain the desired beam spread characteristics. Desirably, the vertical beam spread is about −10° while the horizontal beam spread is about +/−35°.
In view of the foregoing, there exists a need to provide a projector-type headlamp which exhibits improved control over the beam spread characteristics of the outputted light.